[Truncated abstract] Infrared detection finds application in a wide range of fields, including remote sensing, astronomy, medicine and defence. Many of these applications, which require high sensitivity over a specific band of wavelengths, employ infrared systems based on the semiconductor alloy HgCdTe. While the alloy remains the material of choice for short and mid-wave applications, it suffers from a number of limitations for longer infrared wavelengths. One proposed material alternative is the HgTe-CdTe superlattice, which, at these longer wavelengths, exhibits a greater control of cut-o wavelength, a higher absorption coeficient and a reduction in tunneling currents. The HgTe-CdTe superlattice comprises nanometre-thin alternating layers of semimetallic HgTe and wide-gap semiconducting CdTe, and is produced using molecular beam epitaxy (MBE), a state of the art crystal growth process used to deposit layers of single crystal material on a suitable crystalline substrate. In this thesis, MBE has been used to grow a number of HgTe-CdTe superlattices with varying layer thicknesses on (100) and (211) CdZnTe substrates in order to better understand this material system. The optical and electronic properties of the superlattice are governed primarily by the layer thicknesses, and the growth conditions must be carefully monitored and controlled to ensure a uniform, high quality growth. The study of MBE growth and the subsequent material characterisation comprises a significant component of this thesis. A number of structural characterisation techniques were undertaken in this thesis to determine the layer thicknesses, composition, crystal quality and lattice strain. These included optical and electron microscopy, and x-ray di raction. High resolution transmission electron microscopy enabled direct imaging of the superlattice layers, determination of the individual layer thicknesses and estimations of the interfacial grading.
|Qualification||Doctor of Philosophy|
|Publication status||Unpublished - 2010|